Regulation of induction-motor cascades



Aug. 24, 1926. I 1,597,485

' W. SEIZ REGULATION OF INDUCTION MOTOR CASCADES Filed August 13. 1925 Fig. 4.

Inventor I Walter Seiz y I ,A f as Accl Patented Aug. 24, 1926.

WALTER SEIZ, OF BADEN, SWITZERLAND,

ASSIGNOR TO GENERAL ELECTRIC COM- ZBANY, A CORPORATION on NEW YORK.

REGULATION INDUCTION-MOTOR CASCADES.

Application filed August 13,1923, Serial No. 657,227, and in Germany August 23, 1922.

My invention relates to the speed regulation of machines which are used in connection with regulating exciters and in particular to the speed. control of an induction mo- I onthe shaft of the indu ction motor, or comnormal range of speed regulation, .Sll'flble to occas onally go to a tion motor occurring at said speeds.

prises one element of aregulating set, the

size of the commutator machine or the entire regulating set, must be proportioned in accordance with the scope of regulation desired; that is to say, the size and cost of the regulating apparatus is about proportional to the extent of the desired speed regulation figured from the synchronous s eed of the inductionmotor. Itfrequently iappens that with a given cascade having a it is despeed considerably below the normal regulating range. In such acase it would not be good economy to design the regulating exciter or set to take in the lowest speed desired since the size and cost of the regulatingequipment would need toibe materially increased and the necessity for the use of the larger equipment. would be small. The primary objectof my invention is to provide a practical solution for thisproblem. In carrying my invention into effect, the commutator exciter is laid out only for the speed regulating range occurring under normal conditions. Tofregulate the induction motor speed below.this range I provide a resistance to be inserted" into the secondary circuit of the induction motor after the voltage of the commutator machine has been increased to its highest value and thus. after the lowest normal speed of the usual regulating equipment has been reached. For theabnormal low speeds the voltage drop in the resistanceplus the voltage of thecommutator machine is made aboutequal to, the slip voltage of the induc- Thus, the speed of the motor may be regulated below the range of the particular commutator .machine and the total rangeof regulation increased with a smalleroutlay for regulat ing equipment than eommutatormachine'were desig ed to cover.

would be the case if the the entire range of regulation. The electrical. efficiency of such a system when operating below the normal regulating range will be somewhat impaired, but since it is assumed that the low speed operation is needed only occasionally, while the normal regulating range is used most of the time, the loss resulting from the occasional decrease in electrical efficiency becomes insignificant as compared to the saving made by the use of the smaller commutator machine.

The invention also includes a preferred type of equipment for regulating the voltage of the comn'iut-ator machine and the cutting in and out of the resistance combined in such a manner that changes in the speed are accomplished gradually when the resistance is cut in or out, together with automatic devices where they are desired.

The features of my inventionwhich I believe to be novel and patentable will be pointed out in the claimsappended hereto. For abetter understanding of my invention reference is made to the following description taken in connection with the accompanying drawing, Fig. 1 of which represents a complete wiring diagram and layout for a simple embodiment of my invention; Fig. QrepresentS characteristic curves illustrative of the speed regulation obtainable'by my invention; and Figs. 3 and 4 represent preferred forms of the regulator itself, together with certain automatic regulating eatures to be referred to.

. Referring to Fig. 1, a is the induction motor-which is fed (from the power lines b. 0 are the slip rings of the rotor of the induc tion motor, d is the armature and e the ex citer winding of the commutator machine. The armature d can be connected to the slip rings 0 directly or through the resistance 9 by means of a double throw switch 7. "The exciter winding 6 is fed by a regulable transformer h from the slip rings of the induction motor. The normal speed regulation of the motor is effected by the displacement of the movable contacts 6 on the transformor h wl'iereby a more or lessof the slip ring voltage is caused to etlect the exciterwinding 0. ,If these contacts move to the star point of thetransformer, the winding 0 receives Qno excitation, the, commutator machine: has no voltage and the inductionmotor runs approximately synchronous speed wt nxhe resistance 17 i not in circuit.

her end of the transtori'ner Winding, the excite-r winding (2 becomes fully excited, the armature ot the comn'lutator machine gives its highest voltage and the induction motor a has the lowest normal speed. It the speed to he still further reduced. the resistance 5/ will be connected in by means of the switch 7'. The voltage crop of ti e rotor current in resistance 110W added to the voltage oi the counnutator machine or to that component ot this voltage which equal in phase with the slip ring voltage of the induction motor. The ip voltage and tli 1 i'e .vith the slip oi the induction motor vill therefore be increased without requiring a stroi'iger excitation of the commutator machine.

In the foregoing discussion it has been assumed that the commutator machine is connected up as a shunt machine and that its excitation is regulated by i'neans ot adjustable auto-transtoriucr. The invention can, hovvever, be used ii at a. WQll with any other connection ot the cou'unrtator machine such as compound or series connection or with other kinds of regulations such for example as the regulation which can be cttected by brush displacement on the commu tator machine or by the change o t ohmic resistance in any one of a number or an iary circuits assoc'ated With the exciting winding of the conin'iutator machine.

If the increase of the regulating range which is to be obtained by means of the re sistance f] is considerable, then when connecting in the resistance, and particularly when cutting it out, a very unpleasant jump in the POWQI' intake from the line and in the speed of the induction motor will o cur. This jump may be decreased by subdividing the resistance into several steps and connecting the varous portions of the resistance in and out in succession. Sum an arrangement .vould be expensive since appai us iv uld he required including switches vvnich would nece sarily have to arry the full rot current of the induction motor. In cordance with my invention. the resistance is pret'e ably connected in and out as a whole a; el I I'OViSiOD made tor decreasg or avoiding the undesirable jump in the "or intahe of the cascade or in the speed 1e induction motor. To this end, 1 pro- 'ide appa'atus for decreasing or increasing the voltage of the commutator machine at the same time the resistance is cut in tres cctively.

his

or (u -1 Fig. 2 illustrates curves obtained by plot ting speed against the p si n of the volttio age regulator, the sneed being given in percent of the synchronous speed of the induction motor. Curve 1 applies for the norregulation of the set, tl atis to say. When mar the resistance not connected in the rotor circuit. Curves 2 and 3 apply with the re sistance connected in, curve :2 being for a small load and curve f r 2 larger load on the induction motor. In the ligurc it is assumed that the commutator machine. acting alone, has a regulating range oi in 12 steps and that after 'tf-liiiQCl'iW-j in the resistance, with the smaller load on the th step and with the larger load on the zero step of the regulator, the same speed ohtainet. as with the 12th step of the regulator when the resistance is not connected in. It the resistance is connected in on the 12th step of the regulating device. the latter should be set i aclc with the smaller load to the 5th step and with the larger to the first step and then advanced again step by step to the 19th to decrease the speed. la the curves o'l Fig. 2 there is illustrated an increase in the total regulating range tron] 30% to 50)? for the smaller load. or from 30% to 607?, with the larger load and by properly manipulating the reguhit tu'. the entire resistance can be conne'ted in at nce d still avoid a la ge jump in the speed of the induction motor.

The voltage of the con'imutator machine may be regulated manually or autom tially. for em mple in response to the par-fer taken from the line. l ly auti'miatic reculation tho povver taken from the line niav be kept almost evactly constant and t1 automatic voltage regulation can he made independent of the res' tance in the rotor circuit. For it the resistance is conncucd in after the regulating device has rea :hed

last step, either by hand or automatii-ally,

the regulating device will amonuiticaily re turn to the required position illust *atc l hthe curves in It ent re automa c regulation is useth the re ay \vl'iich c ts in the rotor resistance should he interior-lei in some way with the pos'tioa ot the voliag regulator so that when the voltage regulating device is on the last step, the rotor r sistance is cut in. This relay may it sired. be made dependent on ill)" l rotation so that it operates as speed is reached which correspon t last step of the voltage ltjl'tlliltfil'. l a given speed of the induction mot r thc:'e al uys correspojds a given load tl the range of operation, the actua for the speed regulation of the a be further simplified in that the r ot' the voltage of the couunutator ra ch: and the connecting in and out of the r ance of the rotor circuit is ctlectcd by same actuating device.

This is illustrated in Fig. 3 cents one phase of the former,

vh e o 4 la ing I {he and 2' one of the movable co which slide on a contact path 7'. instance the contact path Z contains assumed in. Fig. fund which are 1::

of simplicity, l one ly designated in the two figures. The contact i is displaced with respect to the spindle m by meaus'of a hand wheel Z, the spindle Z being threaded and the contact 2' acting as a nut thereon. A contact operating'lever q pivoted at p is arranged to be moved by the cont-actor 2' so as to close or open the energizing circuit of a contactorswitch f which nowtakes the place of the manually operated switch f of Fig; 1. For the sake p ase of the various circuits has been shown in Fig. 3. When the contact 5 is moved from position 1 toward position 12, the arm n of lever Q will be out of the path of movement of contractor 2' with the short arm of lever 9 against stop 1". The arm 0 of lever q will, however, stand in the path of the movement of contactor i so that lever Q will be turned clockwise when the contactor 2' reaches position 12, contacts 8 will be closed to energize relay f and the resistance 9 will be connected in the rotor circuit of the induction motor. At the same time, the arm n of lever Q will be swung into alinement with the contact 5 so that when the latter is returned toward the zero position and is adjacent position 4, it will turn the lever q in a counter clockwise direction thereby opening the energizing circuit of relay 1 and again establish the normal regulating conditions. vice the regulation has been carried to po-' sition 12, then by further movement of the hand'wheel, contacts 8 will be closed by the actuation of arm 0 and the resistance connected up in the rotor circuit. It will then be necessary to regulate back to position 4' in order to again obtain the same speed as before on position 12.

In such an arrangement quite a strong current and shock will be produced in the mainrmotor when connecting up the resist ance and which only disappears after the regulation has been carried back a few steps. If this regulation is not done quickly, there will also be a jump in the speed of the induction motor. In most cases, it will be desirable to avoid, this jump in current and the shock to the motor and this can be done in accordancewith my invention if the regulating device is arranged so that in regulating the motor from the highest to the lowest weed, the regulator is always moved in the same direction whereby at first the voltage of the commutator machine is increased and then after reaching the highest permissible voltage, the resistance is connected in the rotor circuit and at the same time, by a further movement of the regulator, the voltage of the commutator machine is decreased to a desired value and finally, by a further movement of the actuating device, the voltage of the commutator machine is again in creased with the resistance connected in the rotor circuit.

direction to decree. c

If by this de- Such a regulator is illustrated in Fig. 4, where only one phase of the regulating circuit is shown for the sake of simplicity, the designations in this'figure being the same as those in Fig. 3. The contact path it in Fig. t has 20 steps instead of 12 and contact 1:5 is directly connected with contact 5, 14 with 6, lowvith 7, etc. he relay contacts for controlling the cutting in and out of the resistance in the rotor circuit must be so arranged with this switching device that when advancing from step 12 to step 13 the resistance is connected in and is again disconnected when returi'iing from step 13 .to 12. It is possible by this arrangement to reduce to a minimum the undesirable jumps in current and shocks to the motor. In this modification the lever q for operating the contacts 5 is positioned adjacent contacts 12 and 123 and arranged so that when contact i i" advanced past this point in an upward the motor speed, contacts s are closed while, when the contact 2' is returned, these contacts are opened.

In Fig. at l have illustrated. a reversible pilot motor Z for adjusting the position of the. controller instead of the hand wheel Z snown in Fig. This pilot motor is connected to suitable source, for instance the supply line b of the main motor through a discmjmecting and reversing relay u, the position oi which is made dependent on the value of the line current supplied to the main motor. F or instance, when the line current becomes of such a value as to overload the motor, the relay u is strongly energized and closes the pilot motor circuit through the upper relay contacts, thereby causing the motor Z to rotate in a direction to decrease the main motor speed; WVhen the main motor current is normal, the relay it stands in the intermediate position illustrated with the pilot motor circuit open and when the line current decreases to a low value corresponding to an underload condition of the motor, the lower contacts oi relay 1/, are closed energizing the pilot motor in the reverse direct-ion, thereby causing it to rotate in a direction to increase the.

In accordance 'with the purpose of the invention the load speed of the main motor.

relay a should of course be adjusted to 0btain the least load shock to the apparatus when the resistance 9 cut in. The contacts controlled by the relay u may, it desired, be controlled manually, or'by a centrifugalgovernor driven. from the main motor, or in any other desired manner.

The method explained above for the speed regulation of an induction motor can be advantageously employed in the control of the well known Ilgner converter where the slip resistance of the driving motor of the converter is replaced by acommutator machine connected in cascade with the driv- Ill) ing' motor and provided with the auxiliary a'lpisting resistance hereinbetore described.

it such a converter serves, for example, for the aeration of a rolling mill motor, wherethe load is tilt- (311 oil from the converter '-whcel e cry normal ope sting pass of the mill. however, only to the lowestlimit of the normal regulating range given by the commutator machine alone, then the movable contact on the regulating transformer, referring to Figs. 2 and 3, will be adjusted at every normal operating pass of the mill from the zero position to position 12 and bacl; again. It. however, there occasionally occurs a higher load on the rolling mill, for example, by the introduction of an insufficiently litlttl ingot, then it will become necessary to take a greater power from the tly-wheel and in order to avoid the taking of too at a quantity oit power from the line. the auxiliary resistance g may be iiiscrted in the cascade connection. The automatic control ol the ll gjner converter will then regulate beyond the position 12 in the manner described in connection with l to connect up the auxiliary' resistance g in the rotor circuit whereby a further regulating range becomes available so that an e;- cessive increase of the power taken from the line can be etl ectively prevented with a very small increase in the costof the regulating equipment. The size of the entire Ilgner converter may thus be decreased to that required for normal condition.

n accordance with the provisions of the patent statutes. I have described the princip e ot operation 01" my invention, together with the apparatus which I now consider to rc 'rrcsent the best embodiment thereof, but I desire to have it understood that the apparatus shown only illustrative and that the invention can be carried out. by other means.

What I claim as new and desire to sect re by T etters Patent of the United States, is,-

1. The method of regulating an induction motor cascaded with a regulating exciter which consists in increasing" the excitation of the excitei' to substantially a maximum, thereait'tcr insertingresistance in the eascade circuit and simultaneously decrearing the excitation of the exciter and then iiicreasino' the excitation of the exciter with the res [stance in the circuit,

2. The method oi regulating the induction motor cascade of claim 1. which consists in peritormin; the operations and adjustments of claim 1 in the reverse order and direction respectively.

The met lOCl of regulating an induction motor cascaded with a regnlatine exciter, which consists in increasing" he voltage given by the exciter to substantially a maxi mum. thereafter producing a voltage drop between the induction motor and exciter and simultaneously decreasing the voltage of the cxcilcr a corrcspoinliue amount and then again increasing the voltage of the exciter.

The method of regulating: the iinluction motor .ajle of claim 3, which consists in performing; the operations and adjustments oi claim 3 in the reverse order and direction respectively.

5. in combination a wound secondary induction machine, a rcilulating exciter connected in cascade t'hci 1th. additional regulating; means associated with the cascade tor increasing; the range of regulation; and a common actuator for adjusting both said nitiating; excitcr and additional regulating; means. so arranged that the regulation given by the (.Xv'flttl' becomes substantially a maximum bclore the additional regulating means becomes cil'cctive.

t In coinhi hi .on, a wound secondary induction machine, a regulating cxciter connected in cascade relation therewith. a re- .tr ice. means tor including sa'd resistance in the cascade circuit, means for regulating the voltage said excitcr, said two means being interlocked by a common actuating device in such a manner that the excitation ot said ex 'itcr is increased to substantial a maximum hetore said resistance is inserted and so that the voltage out the exciter is decreased to an amount substantially corresponding to the voltage drop in the resistance when the latter is inserted 7. In combination, an induction machine a regulating exciter cenuewted in cascade relation therewith, a volagre regulator for said exciter having a plurality ot steps, so arranged that when the regulator is moved from one extreme position to the other the voltage of the exciter is first gradually increased and then suddenly decreased and again gradually increased. other means tor producing a voltage drop in the cascade sub stantially corresponding to the said sudden decrease obtained by the voltage egulator, and a. controller actuated by said voltzwe regulator when the suddenly decreasing; voltan'e step is reached itor controlling; said means.

Tn witness whereof, I have hereunto set my hand this 26 day oi Tu v. 1923.

lVALTER SEIZ.

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